There are three basic performance levels in the IR camera market today. First, there are the high performance IR cameras that typically employ IR detectors that are wavelength-selective (e.g., HgCdTe, InSb). These cameras possess several of the following characteristics: high-speed, high-sensitivity, large format, windowing, snapshot mode, and external synchronization. However, they are costly, largely because they require cryogenic cooling (to reduce noise, etc), and HgCdTe is difficult to control during manufacturing. These cameras are typically used in aerospace, military, and research applications. The cost of a high-performance IR camera can range between $70K and $170K. Second, there are the general-purpose IR cameras that are primarily used for predictive maintenance (PM). These cameras must be radiometric but do not require high-speed. The cost of PM cameras range between $40K and $70K. Finally, there are the low-cost uncooled IR cameras, typically based on microbolometer or pyroelectric technology. These cameras detect wavelengths from 3 μm and longer. They operate at low video frame rates and offer a much poorer image due to non-uniformity between pixels. These cameras are used in qualitative applications such as surveillance, fire rescue, and automobile night vision. Uncooled IR cameras cost around $15K. This invention targets the low-cost, uncooled IR detector camera niche. An uncooled IR detector camera that can purchased for around $1000 would be a unique instrument and would revolutionize the IR camera market in much the same way as the development of the uncooled microbolometer camera has over the last five years. Low cost is the key that opens the door to hundreds of markets.
U.S. Pat. No. 6,861,790 to Iwasa teaches a cold cathode element for flat panel displays. The cold cathode element consists of an aluminum substrate on which amorphous carbon film containing cesium is grown using vapor deposition. Several small conical projections of cesium oxide are formed on the film. The “projections” or nanostructures on the substrate are formed of cesium oxide but the type of nanostructure (e.g., nanotube, nanoflake, nanofiber, etc.) is not specified. Iwasa teaches only a basic method of producing low work function field emission and no circuitry for producing a practical device is included.
U.S. Pat. No. 6,400,088 to Livingston et al. teaches an infrared (IR) detector consisting of an anode, a cathode on which is deposited a forest of carbon nanotubes, and bias circuitry for applying an electric field between the anode and the cathode such that when IR photons are absorbed by the nanotubes, photoelectrons are created. Livingston fails to teach that cesium is added to the nanotubes.
U.S. Pat. No. 5,908,699 to Kim teaches a cold cathode element for flat panel displays consisting of an amorphous carbon matrix having cesium dispersed therein, with the cesium present in substantially non-crystalline form. A method of producing the cesium oxide and a method of designing a single electron emission device for improved brightness is also specified.
Field emission properties of carbon nanotubes have been extensively studied for the fabrication of cold cathodes for field emission displays. However, application of this technology to infrared imaging has not been investigated.